a. Field of the Invention
The present invention relates to a process for purifying gases containing H.sub. 2 S or H.sub.2 S and a small amount of SO.sub.2 and preparing, at the same time, elemental sulfur.
B. Description of the Prior Art
With regard to desulfurization of sulfur-containing petroleum fuels, it has been recently disclosed that a method to desulfurize the fuels at petroleum refining plants is preferable to desulfurizing after burning the fuels or so-called stack gas desulfurization as a measure to eliminate environmental pollution caused by sulfur oxides. For the desulfurization of petroleum fuels, hydrogenating desulfurization is generally adopted. For such petroleum fractions to which this method cannot economically applied, a variety of gasificating desulfurization methods have been proposed. In either method, however, sulfur compounds removed are separated from the fuels in the form of hydrogen sulfide or sulfur dioxide. Ordinarily, desulfurizaton is conducted by hydrogenating sulfur in the fuel into hydrogen sulfide, extracting this hydrogen sulfide with solvent, releasing concentrated hydrogen sulfide, and producing sulfur by allowing the hydrogen sulfide to react with sulfur dioxide obtained by burning a part of the hydrogen sulfide by the Claus furnace process. The exhaust gas from this process, however, does not meet the requirements of the pollution prevention regulations since it still contains unreacted hydrogen sulfide and sulfur dioxide. Therefore, disposition of such tail gas containing hydrogen sulfide and sulfur dioxide at present requires more equipment and operating costs than the Claus furnace process.
As a means to solve such problem, the Townsend process has been proposed, which is a process that eliminates the Claus furnace process and serves to dispose of tail gas. To be more precise, it is a closed cycle process that does not release sulfur compounds into the atmosphere, by producing sulfur in a solvent into which hydrogen sulfide coexisting with fuel gas has been extracted. This process is described hereunder in further detail. Ethylene glycols are used as the solvent. Sulfur is precipitated by allowing an absorbing liquid prepared by causing sulfur dioxide to be absorbed by said solvent to react with hydrogen sulfide in the fuel gas in an absorbing column. This reaction that produces sulfur by allowing hydrogen sulfide to react with sulfur dioxide in solvent requires much time. Besides this solvent does not absorb hydrogen sulfide well. For these reasons, it is very difficult to reduce hydrogen sulfide in the fuel gas to a small amount. That is, it is not possible to reduce it to a small amount within ordinary retention time during which solvent passes through the absorbing column. In other words, it is difficult for the absorbing column to provide enough time to effect chemical reaction between hydrogen sulfide and sulfur dioxide in solvent. Furthermore, this solvent does not absorb hydrogen sulfide well, as mentioned before. Accordingly, it becomes necessary to circulate a large quantity of liquid to desulfurize the fuel gas to a degree in compliance with present pollution prevention regulations.
In this process, sulfur dioxide is prepared by burning sulfur produced or untreated hydrogen sulfide, which results in low efficiency since sulfur that is to be recovered as a product and other fuel gases than hydrogen sulfide are also burnt. In addition, this process requires costly equipment since acidic solutions are used in many parts thereof because the solvent having absorbed sulfur dioxide is circulated therethrough. Particularly, the part in which the solvent is purified by releasing sulfur dioxide at high temperature must be made of special materials that are costly.